Heat treatment of steel



Patented Mar. 1 1927.

UNITED STATES- L EDWARD I. IEENNEY, OF BETHLEHEM, PENNSYLVANIA.

HEAT TREATMENT OF STEEL.

No Drawing.

ture, after which it may be cooled to atmospheric temperatures.

- In order that a steel object, such as a rail, 1 I

has the proper combination of hardness and toughness, it is essentialthat it be uniformly eated' above the critical range and then rapidlycooled to a temperature below such range. f In the further cooling ofthe object a temperature range is passed through in which the metal ismore or less plastic and thereby capable of withstanding stresseswithout rupture or serious strains. When the temperature, however, hasdropped as low as ghst blue-heat zone, this plasticity is largely Now ifan object, such as a rail, having some portions substantially thinnerthan others, after being cooled through the'critical range, were allowedto further cool, uncontrolled, to atmospheric temperatures, naturallythe thinner portions would cool "much more rapidly than the thicker andwould enter the blue-heat zone much sooner. At this stage the plasticityof the thinner portions would be much reduced, while the thickerportions at a substantially higher temperature would still be in theplastic stage. Consequently, upon further cooling of the thickerportions with resulting con traction, the thinner portions of the metalnow being low in plasticity, stresses are set up which produce seriousstrains and even rupture.

To control the cooling and thereby prevent this condition is the purposeof my invention.

My invention may be best illustrated by setting forth several specificexamples.

Rails of the following composition-Carbon .63 to .87, manganese .60 to.90, phosphorus .03, sulphur .05, and silicon .15 to .25 were quenchedin water for about thirty seconds from a temperature about 17 50 F.,

Application filed April 23,

HEISSUED bringing the temperature down to about 725 F., the cooling thusbeing from a temperature above the critical range to one below it butabove the blue-heat range. The rails were then charged immediately intoa furnace maintained at 1000 F. They were kept at this temperature onehour and then removed from the furnace and allowed to.

cool in the air. Under. the drop test these rails were tougher than theregular rail which has not been quenched and they showed no sign ofruptures.

Rails of the following composition- Carbon. 935? 233; Sulphur. Silicon.

were also treated by quenching from a temperature of 1550 F., thequenching stopped before the blue-heat zone was reached, and immediatelyequalized at 900 F. I

Extensive tests were made upon these rails, including drop tests,Brinell hardness tests, Izod impact tests, and macroscopic andmicroscopic examinations. The physical properties were greatly improvedand no signs of internal ruptures found;

On the other hand, when rails of the same compositions were quenched inthe same way but without being given the equalization treatment betweenthe critical range and the PATENT OFFICE.

blue-heat zone, the metal structure was found to be badly ruptured.

For example, i quenched from a temperature of 1750 in water for 2minutes, bringing them nearly tov atmospheric temperature. These railsbroke into a number of fragments before they were removed from thequenching tank.

Again, rails were quenched in water from a temperature of 1750 andthenallowed to cool in air, there being no equalization treatment. Theserails cracked in cooling and when out up and ex amined macroscopicallyand microscopical-- ly were found to be badly ruptured nternally as wellas externally.

It is economically advantageous to carry out my process in connectionwith "the mechanical working. For example, in the manufacture of railsafter leaving the rail mill some of the rails were.

F. for 30 seconds" .ized the rails'are quenched to a temperature abovethe critical range. This equalizing chamber will, of course, be main-'tained at the desired temperature by any suitable heating means. Afterbeing equaltemperature below the critical range but above the blue-heatzone. Without allowing them to cool they are immediately charged into afurnace kept at a temperature preferably be tween 800 and 1100 F. andkept there until the temperature is thoroughly equalized. Then, afterstraightening, they are allowed to cool to atmospheric temperature. Ofcourse all the details here mentioned are not always essential. Forexample, the equalizing before the quenching may be omitted; i

The choice of temperature for, equalizing, after the uenching operation,varies with the particu ar combination of hardness and toughnessdesired.

What I mean by the blue-heat zone, as this expression is used in thisdisclosure, is that range of temperatures, below the critical rangewhere steels in heating markedly increase in tensile strength and theelastic limit, and also markedly decrease in ductility. At temperatures,within this range, most steels when ex osed to air take on a blue color,due to oxidation, but since, with some steels, this color is not readilyap parent, I do not wish to be limited to the color as a means ofdetermining or defining this zone.

that temperature range through which'the steel must be cooled to effecta hardening thereof. This range will vary with the particularcomposition of the steel, the varlous ranges'according to. diflerentcarbon c0ntents being in the common-nomenclature A A3 2: and s 2 1-Having thus described the invention what I claim as new and desire tosecure by Letters Patent is:

1. The process of heat treating a steel object which consists in rapidlycooling it from a temperature above to a temperature below the criticalrange, then equalizing at atemperature'below the critical range butbefore the object has cooled to the blue-heat zone, and then cooling toatmospheric temperature.

2. The process of making a steel object of irregular shape,. consistingin mechanically shaping the steel, in cooling rapidly from above tobelow the critical range before the object has lost the heat incidentalto shaping, equalizing at a temperature between the critical range andthe blue-heat zone before By the expression critical range I mean theobject has cooled to the blue-heat zone,

and cooling to atmospheric temperature. In testimony whereof Ihereunto-aflix my signature this 20th da of April, 1926.

EDW D F. NEY.

